1. Technical Field
The present invention relates to a projection image display position control device, a projection image display position control method, and a projection system.
2. Related Art
A method for performing stack projection of identical images on one screen (projection surface) by using a plurality of projectors is known. When pixels on the projection image from one of the plural (two in this case) projectors are matched with the corresponding pixels on the projection image from the other projector in the stack projection, the luminance of the projection images on the screen is substantially doubled, and thus high-luminance image display can be achieved. Moreover, when the corresponding pixels are shifted by ½ pixel in the vertical and horizontal directions, highly minute image display can be produced.
In case of the stack projection described above, however, it is not easy to accurately display the projection images from the two projectors at target display positions (display target positions) specified for each of the projection image on the screen. When the projection images from the plural projectors are not displayed at the display target positions, the image quality of the projection image deteriorates. For example, when the projection images from the two projectors are shifted by ½ pixel for highly minute projection, the advantage of highly minute projection cannot be achieved without accurate display position control for accurately shifting the respective pixels on the projection images from the projectors by ½ pixel. In this case, there is also a possibility that noise such as moiré is caused on the image which is originally free from such noise.
Various types of methods for accurately setting the display positions of the projection images from the plural projectors have been proposed (for example, see JP-A-8-168039). According to the technology disclosed in JP-A-8-168039 (hereinafter referred to as related art), the display position shift amount between the two projectors is calculated, and the display position shift amount is mechanically controlled by using a display position control mechanism. In the related art, a display position control mechanism capable of controlling the clearance between wedge-shaped transparent substrates, a display position control mechanism capable of controlling rotation angle of a flat-plate transparent substrate, a display position control mechanism capable of shifting an actuator-attached optical stage in a parallel direction, and other mechanisms are shown as examples of the display position control mechanism.
FIGS. 4A and 4B illustrate a display position control mechanism shown in the related art as an example. FIG. 4A shows an example of the display position control mechanism for clearance control between wedge-shaped transparent substrates, and FIG. 4B shows an example of the display position control mechanism for rotation angle control of a flat-plate transparent substrate.
As illustrated in FIG. 4A, the display position control mechanism for clearance control of the wedge-shaped transparent substrates can displace the optical axis of the projection image from the projector by a predetermined amount by increasing or decreasing a distance d between wedge-shaped transparent substrates 1a and 1b. In this structure, a displacement amount s of the optical axis can be arbitrarily set within a predetermined range by controlling the distance d.
As illustrated in FIG. 4B, the display position control mechanism for rotation angle control of the flat-plate transparent substrate changes a rotation angle θ of the flat-plate transparent substrate 2 to displace the optical axis of the projection image from the projector by a predetermined amount. Thus, the displacement amount s of the optical axis can be arbitrarily set within a predetermined range by controlling the rotation angle θ.
According to the display position control mechanism capable of shifting the actuator-attached optical stage in the horizontal direction which is not shown in the figure, the displacement amount of lights can be arbitrarily set within a predetermined range by shifting the actuator-attached optical stage in the horizontal direction by a predetermined amount.
According to any of the display position control mechanisms discussed above, the display position of the projection image can be controlled both in the horizontal and vertical directions.
Any types of the display position control mechanisms used in the related art described above can vary a displacement amount s of the optical axis. Thus, the display position shift amount from the display target position is not limited to an integer number times larger than the pixel pitch, i.e., the unit of 1 pixel, but may be values containing decimals such as “0.3 pixel” and “1.2 pixel”. In any display position control mechanisms discussed above, however the movable range of the display position control mechanism needs to be sufficiently wide when a large shift of the display position is controlled. In this case, the size of the projector increases.
More specifically, in case of the display position control mechanism for controlling the distance between the wedge-shaped transparent substrates 1a and 1b, the distance d similarly needs to be long so as to increase the displacement amount s. For satisfying this requirement, at least the movable range of one of the two wedge-shaped transparent substrates 1a and 1b needs to be sufficiently wide. In addition, for increasing the distance d, a width L of the wedge-shaped transparent substrates 1a and 1b needs to be large.
According to the display position control mechanism for controlling the rotation angle of the flat-shaped transparent substrate 2, the rotation angle θ needs to be large so as to increase the displacement amount s. In this case, the movable range of the flat-plate transparent substrate 2 needs to be wide. In addition, an expected width L0 in the projection direction decreases as the rotation angle θ increases. Thus, a length L1 of the flat-plate transparent substrate needs to be long.
According to the display position control mechanism for shifting the actuator-attached optical stage which is not shown in the figure, the movable range of the actuator-attached optical stage needs to be sufficiently wide so as to increase the displacement amount.
Alternatively, display position control may be performed through image processing. According to the display position control method by the image processing, the necessity for the display position control mechanism is eliminated, and increase in the size of the projector is prevented. However, there is a possibility of deterioration of image quality caused by image processing.
More specifically, the display position control through image processing shifts pixels when the display position is adjusted by the unit of 1 pixel, that is, by an integer number times larger than 1 pixel. Thus, the display position control can be easily and highly accurately performed. However, the display position control through image processing is generally controlled by interpolation when the display position is adjusted by a value smaller than 1 pixel. In this case, image quality deteriorates.
For example, when a linear image A (see FIG. 5A) having a width of 1 pixel is shifted to the left in the figure by ½ pixel as illustrated in FIG. 5A, a process for displaying a linear image shifted by ½ pixel is performed by using adjoining two pixels. Thus, the linear image A originally having the width of 1 pixel is represented as a linear image A′ (see FIG. 5B) having the width of two pixels, and the image quality thus deteriorates. In FIGS. 5A and 5B, each of small squares corresponds to one pixel of the optical modulation element of the projector.